JPS59137961A - Electrophotographic offset printing original plate - Google Patents

Abstract

PURPOSE:To obtain good electrophotographic characteristics in an electrophotographic offset printing original plate forming a photoconductive layer on a precoat layer formed on the surface of a conductive substrate by forming the precoat made of specified components. CONSTITUTION:A precoat layer is formed by coating a conductive substrate with a coating liquid comprising a pigment contg. a sericite component, a synthetic resin emulsion contg. reactive hydroxyl or carboxyl groups, a melamine early- stage condensate, and a catalyst hardening said condensate, and drying. This precoat layer is excellent in both of resistances to water and org. solvents, and the obtained plate is always stable and it forms a sharp image, and further, causes no extension of plate size during printing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an original plate for electrophotographic offset printing.

In general, electrophotographic materials are used as offset printing plates by forming an image on the photoconductive layer by passing a photoconductive substance and a binder onto the surface of a support that has been subjected to conductive treatment. It is widely used in the field of light printing because the plate-making operation is simple, quick, and inexpensive.

An original plate for electrophotographic offset printing is required to have properties as an original plate for offset printing in addition to properties as a general electrophotographic copying material. This means that the photoconductive surface must be wetted with a special aqueous surface treatment solution, a so-called etchant, so that its non-imaged surface becomes ``grease-free'' after imaging, and large amounts of wetting are used during offset printing. Since water is used, the original plate for offset printing is required to have excellent water resistance, and is also required that the photoconductive layer does not peel off during printing.

In response to these demands, many proposals have been made in the past to provide a precoat layer on a conductive support before forming a photoconductive layer on the support, and to form a photoconductive layer on this precoat layer. .

In addition to the requirements for the above-mentioned properties such as water resistance, this precoat layer is made of an aromatic hydrocarbon solvent so that the coating liquid for forming the photoconductive layer has a photoconductive substance dispersed in a binder resin. Next, there are products that have excellent organic solvent resistance. required.

It is desirable for both water resistance and organic solvent resistance to be at a high level, but in general, water resistance and organic solvent resistance are mutually contradictory properties, so the precoating methods proposed so far As yet, there is no layer that completely meets these requirements, and due to the insufficient level of their properties and the poor balance of their properties, only master plates for electrophotographic offset printing can be obtained that have various drawbacks. This is one of the most difficult techniques for those skilled in the art.

Japanese Patent Publication No. 40-18708 discloses that the water resistance and organic solvent resistance of the precoat layer can be improved by using film-forming resins having reactive hydroxyl or carboxyl groups, such as copolymers of styrene, hexyl acrylate, acrylonitrile, methacrylic acid, and polyvinyl alcohol. , a copolymer of carboxylated p-styrene and maleic anhydride, a copolymer of carboxylated ethylene and maleic anhydride, a hydroxyethyl cellulose, a copolymer of crotonate and vinyl toacetate, etc., as dimethylolmelamine, dimethyl Trime fyw-
It has been proposed to solve the problem by cross-linking with an initial condensation product such as lumelamine or urea-formaldehyde to make it water-insoluble. The present inventors have confirmed that even though the precoat layer obtained by fc is water resistant in the sense that it does not dissolve in water, it cannot completely prevent water from penetrating.

Good water resistance is also required for the backcoat layer, usually the conductive layer. Since a relatively large amount of conductive agent is used in the conductive backcoat layer, it is difficult to prevent penetration of an etchant or dampening solution. Therefore, in order to reduce the amount of the conductive agent in the conductive layer as much as possible, it is possible to impregnate the paper support with inorganic salts or to include the conductive agent in the precoat layer in view of the electrophotographic properties. If it is contained, the water resistance will be poor.

Therefore, the present inventors developed an original plate for electrophotographic offset printing in which a photoconductive layer is formed on the surface of a conductive support via a precoat layer. molecular compounds,
It has been found that an original plate for electrophotographic offset printing having good properties can be obtained by applying and drying a coating liquid consisting of an insolubilizing agent and a conductive agent for the water-soluble polymer compound. (#!f) Slight plate elongation was observed during printing.

An object of the present invention is to provide an original plate for electrophotographic offset printing that has good electrophotographic properties and has a precoat layer that does not cause plate elongation during printing.

The above object of the present invention is to provide an original plate for electrophotographic offset printing in which a photoconductive layer is formed on the surface of a support via a precoat layer, and the precoat layer is composed of a pigment containing a sericite component, a reactive hydroxyl group or a carboxyl group. A coating liquid containing a resin emulsion, a melamine resin initial condensate, and a catalyst for curing melamine, which has good electrophotographic properties by coating, drying, and forming, and is used for electrophotographic offset printing without plate elongation during printing. It was discovered that the original plate can be obtained.

A synthetic resin emulsion in which the inorganic pigment containing the sericite component used in the present invention has a reactive hydroxyl group or carboxyl group], together with the melamine resin initial condensate and the melamine curing catalyst, improve the water resistance and organic solvent resistance of the precoat layer. It is unclear why both are excellent, yet stable and clear images are always obtained, and no plate elongation occurs during printing. Even better - has an experimental backing that can be agglomerated.

Sericite is also called sericite, and its chemical composition is close to that of muscovite, but it is a very fine mica that shows slight changes compared to the ideal chemical composition of muscovite, and its composition differs depending on the place of production and condition. The ideal chemical composition of 0 muscovite with K, 0.3A120t.6 SiOyi.2H! 0, but sericite is 5ins/A compared to muscovite.
The ratio of l2O is large (te, K!O is small, HlO(10
It is characterized by a large amount of water (released at temperatures above 5°C).

In the chemical composition of sericite, potassium is loosely contained between the crystal layers (
Because they are sandwiched, the crystal particles tend to peel off at that part,
That is, it is easy to "fold between folds" and physically exhibits "lubricity." The external shape of sericite is a hexagonal plate-like crystal, and the height of the unit crystal is IO
It is A.

In the present invention, it is preferable to use pure sericite, but from the viewpoint of cost and liquid properties, it may be mixed with other pigments such as kaolin, calcium carbonate, aluminum hydroxide, etc., or an inorganic pigment containing a sericite component may be used. You may do so. In this case, the content of the sericite component is preferably 30% or more, particularly preferably 50'% or more.

The synthetic resin emulsion having a reactive hydroxyl group or carboxyl group used in the present invention includes vinyl groups such as acrylic acid or its ester, methacrylic acid or its ester, vinyl chloride, vinylidene chloride, vinyl acetate, acrylonitrile, butadiene, and styrene. Examples include water-dispersible emulsions having reactive hydroxyl groups or carboxyl groups obtained by emulsion polymerization or emulsion copolymerization of monomers having the following.

The melamine resin initial condensate used in the present invention includes:
Dimethylolmelamine, dimethyltrimethylolmelamine, trimethylolmelamine, tetramethylolmelamine, tetramethylpentamethylolmelamine, tetramethylhexamethylolmelamine, pentamethylpentamethylolmelamine, pentamethylhexamethylolmelamine, other alkylated melamines formaldehyde resins Alternatively, a mixture of these resins can be mentioned.

Catalysts for curing melamine include ammonium salts such as ammonium chloride and ammonium phosphate, organic amines and their salts such as triethanolamine, organic acids and their salts such as sulfanilic acid, chloride, and inorganic metals such as calcium. I can give you some salt.

Further, as components of the brecoat layer of the present invention, conductive agents such as polyvinyltrimethylammonium chloride, polyvinylbenzyltrimethylammonium chloride, polyelectrolytes such as polystyrene sulfonate sodium or ammonium salts, polyacrylates, or inorganic salts such as chlorides, and starch. , casein, polyvinyl alcohol, styrene-maleic anhydride copolymer, and other water-soluble polymer compounds may be added.

By adding a conductive agent, it is possible to obtain a good image free of capri, especially at low humidity, but on the contrary, the printing durability may be reduced.

Due to the sericite component in the inorganic pigment, the pre-coat layer of the present invention allows a good image to be obtained without any decrease in printing durability even when a certain amount of conductive agent is used.

The original plate for offset printing of the present invention has its characteristics in the precoat layer, and any conventionally known materials can be used as the photosensitive layer and support.

For example, the photosensitive layer is made of a photoconductive material such as zinc oxide, a resin, a sensitizing material, etc., and the weight ratio of zinc oxide to resin is usually about 3:1 to 6:1. In addition, as a resin,
Acrylic copolymer, silicone resin, vinyl acetate resin,
Polyester pads such as styrene-butadiene copolymer and nylon are used.

In addition, as a support, for example, a back coat layer is provided on the back surface of a substrate such as paper (the surface opposite to the surface on which the precoat layer and the photosensitive layer are laminated) to impart conductivity and further prevent curling; Alternatively, a substrate may be further provided with an adhesive layer made of polyvinyl alcohol or the like on the surface thereof.

In order to impart electrical conductivity, the above-mentioned electrically conductive agent can be used as a component of the back coat layer. Note that by using a conductive agent in the pre-coat layer and, in addition, using a conductive paper support impregnated with necessary inorganic salts, the amount of conductive agent used in the conductive back-coat layer can be controlled relatively. It has the advantage of being able to reduce the weight of the backcoat layer, thus reducing the disadvantages based on the water resistance of the backcoat layer.

The precoat layer in the method of the invention does not exclude the use of other ingredients, such as dispersants, antifoaming agents, etc.

The precoat layer according to the present invention has a dry coating weight of 3 to 30 g.
/ze, preferably in the range of 5 to 20117 m', is coated by a conventional method and dried.

The present invention will be explained below using examples.

Example 1 was applied and dried so that the dry coating amount was 13 g/m 2 .

[Coating liquid for forming back coat layer]

Kaolin (50% water dispersion, black market name Hydrasperse,
200 parts by weight of oxidized starch (10% aqueous solution) 60 SBR latex (
Solid content 48%) 150# Polystyrene sulfonate ammonium 6o (Solid content 30%)
l Melamine resin initial condensate 4 (solid content 80
%, trade name Sumire Fresin-613 manufactured by Sumitomo Chemical ■) On the other hand, apply a coating solution for forming a precoat layer with the following composition to the front side of the paper so that the dry coating amount is 151/lrl, dry it, and write the l record. After supercalendering the layer surface (surface resistivity 7×10 Ω·min, 20° C., 60% RH), a photoconductive layer was formed on the surface.

[Coating liquid for pre-coat layer formation]

Sericite content: 95% Inorganic pigment: 200 parts by weight (5
0% aqueous dispersion, trade name Selicron, manufactured by Murakami Clay ■) Carboxyl-modified SBR latex 125 parts by weight (
Solid content #s%) Melamine resin initial condensate - 4 parts by weight (solid content 80 cm, trade name Sumire Presin-613, manufactured by Sumitomo Chemical ■) Organic amine salt catalyst 0.4 parts by weight (solid content 35 cm, Product name Sumitex Accelerator AOX, manufactured by Sumitomo Chemical ■) Sodium polystyrene sulfonate 4 parts by weight (solid content 30%)
) A coating solution for forming a photoconductive layer having the following composition was coated at a dry coating amount of about 201/lrl and dried.

[Coating liquid for forming photoconductive layer]

Zinc oxide for electrophotography 200 parts by weight Acrylic resin (50% liquid) 80 l Rose Bengal (
2% methanol solution) 157 xylene
250 The surface coated with the photoconductive layer had no cracks or pinholes (it had a uniform surface quality).

This electrophotographic offset printing original plate was heated to 60% F at 20°C.
Seasoned under JH and 20% plate conditions, and plate-made using an electrophotographic plate making machine Diafax EP-11 (manufactured by Mitsubishi Paper Industries, liquid development plate making machine) to obtain a printing plate with a width of 279 N and a length of 390 mm. .

Next, it was desensitized using an etchant Diafax LPM-OH (manufactured by Mitsubishi Paper Industries, Ltd.) for electrophotographic offset masters, and printed with an offset printing machine Toko Mode 1810 (manufactured by Tokyo Aircraft Instruments, Ltd.).

Under both 60% dish and 20% dish conditions, no capri or other defects were observed (clear images with high sensitivity were obtained. Even after processing with the etchant, no curls or the like occurred, and the process was smooth and easy to operate. The printing plate obtained by the present invention does not cause plate elongation or peeling of the photosensitive layer, even when printing with dampening water and printing more than 5,000 sheets. was confirmed to be extremely excellent.

Furthermore, after putting this original plate for electrophotographic offset printing in a black polyethylene bag and storing it at a temperature of 20°C and 60% RH for one year, it was made into a plate in the same manner as above, and offset printing was performed. After printing 5000 sheets. However, there was no occurrence of plate elongation, photosensitive layer peeling, etc., and no deterioration due to storage was observed.

Comparative Example 1 The sericite content of the pre-coat solution in Example 1 was mixed with the same amount of kaolin (trade name: Haihan≠Table≠隘YO輼). Example 2 The sericite of Example 1 was mixed with the same amount of kaolin. - Printing plates were prepared in the same manner as in Example 1, and almost the same results as in Example 1 were obtained.

Comparative Example 2 A high-density, clear image was obtained. However, in offset printing, plate elongation was observed up to 3000 sheets, confirming the superiority of the printing vein of Example 1.

Comparative Example 3 The melamine resin initial condensate and catalyst of Example 1 were mixed with the same amount of polyamide resin (trade name: Violet), and the results are summarized in Table 1.

Claims (1)

[Claims] 1. A synthetic resin emulsion having phoxyl groups, a melamine resin initial condensate, and a catalyst for curing melamine, on a support. An original plate for electrophotographic offset, characterized in that it is used.